Distal Cantilever Research Articles

Effect of Inter-Implant Distance on Fracture Resistance of Implant-Supported Provisional Fixed Dental Prosthesis.

This study aimed to identify the ideal interimplant distance for optimum outcome on immediately loaded implant supported prosthesis. Hence this study was taken up to analyze the effect of varying interimplant distance on fracture resistance of implant supported provisional fixed dental prosthesis (FDP). A total of 24 bis-acrylate composite resin samples were prepared. Interimplant distance was present in the metal die for placement of dummy implants at distances of 14 mm, 21 mm, and 30 mm respectively. Wax-up for 3-unit, 4-unit, and 5-unit implant-supported provisional restoration was made. Silicone molds were used for making multiple interim prostheses using bis-acrylate composite material. All samples were subjected to fracture test in the universal testing machine with a crosshead speed of 1 mm/min. All samples were loaded with gradual force starting from 100 N until it fractured. The load was applied at the center of prosthesis. Data was analyzed by one-way analysis of variance and Bonferroni post hoc test. Mean fracture resistance of 3-unit provisional FDP at 14 mm of interimplant distance showed 1342.61 ± 179.15 N. Mean fracture resistance of 4-unit provisional FDP at 21 mm of interimplant distance showed 1420.44 ± 170.37 N. Mean fracture resistance of 5-unit provisional FDP at 30 mm of interimplant distance showed 791.61 ± 203.59 N. Both 14 mm and 21 mm of interimplant distance are suitable span lengths to be considered for the optimum outcome during immediately loading with implant-supported provisional restorations. Limitations of the study were that force application was static in nature and not dynamic and the arch form was not "U" shaped but longitudinal using Bis-Acryl material only with no cantilever. Future studies can be done to evaluate the fracture resistance of bis-acrylate material considering biomechanics and arch form of natural dentition. Distal cantilever should be considered along with different material for fabricating provisional restoration.

Effect of Cantilever Extension on Bone Loss in Mandibular Complete-Arch Implant-Supported Fixed Prostheses with Three and Four Implants.

To compare the peri-implant bone loss of mandibular complete-arch implant-supported fixed prostheses (FPSs) supported by three and four implants and to correlate with the size of the horizontal and vertical distal cantilever at prosthesis placement (T1) and after 1 year (T2). A total of 72 external hexagon (EH) type implants were placed in 20 participants. Of these, 24 supported an FPS with three implants (G3I) and 48 with four implants (G4I). The mandibular implants were named 1, 2, 3, and 4 according to their location in the arch, in a clockwise direction. Digital periapical radiographs were taken at times T1 and T2 for analysis and measurement of peri-implant bone loss. The horizontal and vertical distal cantilevers were measured with a digital caliper and correlated with peri-implant bone loss. The survival rate of implants in G3I was 91.66%, and in G4I it was 97.91%. The mean bone loss in G3I was 0.88 ± 0.89 mm, and in G4I it was 0.58 ± 0.78 mm (P = .225). There was no correlation between distal horizontal cantilevers and bone loss in the studied groups, with G3I being -0.25 (P = .197) and G4I -0.22 (P = .129). Larger vertical cantilevers of implants 1 (P = .018), 3 (P =.015), and 4 (P = .045) correlated with greater bone loss in G4I. The number of implants in an FPS did not influence peri-implant bone loss after 1 year of follow-up. Larger vertical cantilevers influenced greater bone loss in complete-arch implant-supported fixed prostheses supported by four implants.

The influence of the number of loaded teeth on the distribution of occlusal vertical forces in onesided dental bridges with one distal cantilever

Aim: The paper aims to analyze the distribution of occlusal vertical forces on the abutment teeth in singlesided dental bridge constructions, in slightly shortened dental arches with one distal extension/cantilever, depending on the number of occlusal units. Materials and methods: In five mathematical models with a slightly shortened dental arch in the lower jaw, a single-sided dental bridge was constructed with 5 abutment teeth and one distal cantilever. A finite element method (FEM) was applied. Occlusal loading was done with simulated occlusal vertical forces of 0.5- 512N. Forces were applied on the occlusal surfaces of the teeth. The loading was done as follows: in Model 1 – on the distal cantilever, in Model 2 - on the distal cantilever and the distal abutment tooth, in Model 3 - on the distal cantilever and the two distal abutment teeth, in Model 4 - on the distal cantilever and the three distal abutment teeth, in Model 5 - on the distal cantilever and all abutment teeth. Distributed forces are measured at the level of the periodontal ligament (PDL). Results: The percentage comparison of distributed forces on the abutment teeth in the examined models 1, 2, 3, 4 and 5 indicates a different distribution of occlusal vertical forces between the models. The most even distribution of the percentage of occlusal vertical forces was observed in model 5, followed by Model 4 and Model 3, while the most unfavorable distribution was noted in model 1 and model 2. In all 5 models, the highest percentage of force is distributed on the distal abutment tooth, with the highest percentage noted in model 1. As the number of loaded teeth increases in models 2, 3, 4 and 5, the percentage of distributed force decreases with the lowest percentage of distributed forces found in model 5. There is a significant difference in the distributed forces percentage values on the distal abutment tooth in model 1 and model 5. In Model 1 it ranges from 92.39% to 148.45%, and for Model 5 from 38.09% to 48.02%. In Model 5 and model 4, the direction of the distributed force in all teeth aligns with the direction of the applied force, which means that the fixed construction in models 4 and 5 is the most stable. Conclusion: The percentage of distributed forces on the abutment teeth is in correlation with the number of teeth loaded. In order to achieve a well-balanced, single-sided dental bridge construction in slightly shortened dental arches with one distal cantilever, the occlusal load must be applied on at least three distal abutment teeth.

Biomechanical behavior of implant retained prostheses in the posterior maxilla using different materials: a finite element study.

The aim of this study is to evaluate the biomechanical behavior of the mesial and distal off-axial extensions of implant-retained prostheses in the posterior maxilla with different prosthetic materials using finite element analysis (FEA). Three dimensional (3D) finite element models with three implant configurations and prosthetic designs (fixed-fixed, mesial cantilever, and distal cantilever) were designed and modelled depending upon cone beam computed tomography (CBCT) images of an intact maxilla of an anonymous patient. Implant prostheses with two materials; Monolithic zirconia (Zr) and polyetherketoneketone (PEKK) were also modeled .The 3D modeling software Mimics Innovation Suite (Mimics 14.0 / 3-matic 7.01; Materialise, Leuven, Belgium) was used. All the models were imported into the FE package Marc/Mentat (ver. 2015; MSC Software, Los Angeles, Calif). Then, individual models were subjected to separate axial loads of 300N. Von mises stress values were computed for the prostheses, implants, and bone under axial loading. The highest von Mises stresses in implant (111.6MPa) and bone (100.0MPa) were recorded in distal cantilever model with PEKK material, while the lowest values in implant (48.9MPa) and bone (19.6MPa) were displayed in fixed fixed model with zirconia material. The distal cantilever model with zirconia material yielded the most elevated levels of von Mises stresses within the prosthesis (105MPa), while the least stresses in prosthesis (35.4MPa) were recorded in fixed fixed models with PEKK material. In the light of this study, the combination of fixed fixed implant prosthesis without cantilever using a rigid zirconia material exhibits better biomechanical behavior and stress distribution around bone and implants. As a prosthetic material, low elastic modulus PEKK transmitted more stress to implants and surrounding bone especially with distal cantilever.

Load bearing capacity of 3-unit screw-retained implant-supported fixed dental prostheses with a mesial and distal cantilever on a single implant: A comparative in vitro study

ObjectivesTo assess the mechanical durability of monolithic zirconia implant-supported fixed dental prostheses (iFDP) design on one implant, with a distal and a mesial extension cantilever bonded to a titanium base compared to established designs on two implants. Materials and methodsRoxolid Tissue level (TL), and tissue level x (TLX) implants were used to manufacture screw-retained 3-unit iFDPs (n = 60, n = 10 per group), with following configurations (X: Cantilever; I: Implant, T: Test group, C: Control group): T1: X-I-X (TL); T2: X-I-X (TLX); T3: I–I-X (TL); T4: I–I-X (TLX); C1: I-X-I (TL); C2: I-X-I (TLX). The iFDPs were thermomechanically aged and subsequently loaded until fracture using a universal testing machine. The failure load at first crack (Finitial) and at catastrophic fracture (Fmax) were measured and statistical evaluation was performed using two-way ANOVA and Tukey's post-hoc tests. ResultsThe mean values ranged between 190 ± 73 and 510 ± 459 N for Finitial groups, and between 468 ± 76 and 1579 ± 249 N for Fmax, respectively. Regarding Finitial, neither the implant type, nor the iFDP configuration significantly influenced measured failure loads (all p > 0.05). The choice of implant type did not show any significant effect (p > 0.05), while reconstruction design significantly affected Fmax data (I–I-Xa < X-I-Xb < I-X-Ic) (p < 0.05). The mesial and distal extension groups (X-I-X) showed fractures only at the cantilever extension site, while the distal extension group (I–I-X) showed one abutment and one connector fracture at the implant/reconstruction interface. ConclusionResults suggest that iFDPs with I-X-I design can be recommended regardless of tested implant type followed by the mesial and distal extension design on one implant abutment (X-I-X).

A Systematic Approach to Restoring Full Arch Length with Maxillary Fixed Implant Reconstruction: The PATZi Protocol.

The traditional configuration of four maxillary implants to restore full-arch maxillary fixed implant prostheses is not without pitfalls. Intraoperative variability, such as bone quality and quantity, may lead to unexpected intraoperative challenges that may not allow for execution of the original treatment plan. Additionally, extensive maxillary sinus pneumatization may inhibit posterior spread and lead to a shortened dental arch or excessive cantilever forces. The PATZi protocol is a systematized algorithm for maxillary full-arch implant treatment planning that addresses such intraoperative surprises and achieves full arch length in the planned prosthesis. PATZi also assigns a numbering classification to each implant configuration, which leads to uniform communication and grading of surgical difficulty, as well as predictable planning for developing future salvage plans. By using the PATZi protocol as a guideline, the surgeon may improve composite torque value and anteroposterior (AP) spread, eliminate distal cantilever forces, and ultimately improve the predictability of the prosthetic treatment plan.

Precision of polyether ether ketone (PEEK) or cobalt-chrome implant bar fit to implants after mechanical cycling.

The aim of this study was to evaluate the fit accuracy of dental implant bars made of either PEEK or cobalt-chrome submitted to cycling mechanics. This was an experimental in vitro study, where units were treated with two implants and mini-abutments, joined by cobalt-chrome or polyether-ether-ketone PEEK bars. A total 20 bars were prepared (n=10 per group) and subjected to mechanical cycling tests (1 million cycles on the distal cantilever of the bar in the vertical direction, 120N and sinusoidal loading, at a frequency of 2Hz). The fit at the abutment/implant interface was measured before and after cycling, and the counter-torque of the vertical screw of the mini abutments was measured after cycling, using a digital torquemeter. Data were analyzed by three-way ANOVA and Tukey's test at 5% significance level. No statistically significant interaction was found among the three factors considered (bar material, implant positioning and mechanical cycling) (p = 0.592). No significant difference was identified in the interaction between bar material and implant positioning (p = 0.321), or between implant positioning and mechanical cycling (p = 0.503). The association between bar material and mechanical cycling was statistically significant (p = 0.007), with the cobalt-chrome bar resulting in greater misfit with mechanical cycling. There was no difference in counter-torque values between groups. The PEEK bar provided better fit of the mini abutments to the implants, even after mechanical cycling. The counter-torque of the screws was similar in all scenarios considered.

Treatment alternatives for the rehabilitation of the posterior edentulous maxilla.

Rehabilitation of the edentulous maxilla with implant-supported fixed dental prostheses can represent a significant clinical challenge due to limited bone availability and surgical access, among other factors. This review addresses several treatment options to replace missing teeth in posterior maxillary segments, namely the placement of standard implants in conjunction with maxillary sinus floor augmentation, short implants, tilted implants, and distal cantilever extensions. Pertinent technical information and a concise summary of relevant evidence on the reported outcomes of these different therapeutic approaches are presented, along with a set of clinical guidelines to facilitate decision-making processes and optimize the outcomes of therapy.

Distal cantilever length comparison in esthetic material for hybrid implant prosthesis: an in vitro study.

Objective: the assessment of distal cantilever length in implant supported prothesis (Hybrid prosthesis) by comparing the load to fracture in two different esthetic framework materials (Zirconia and Polyetheretherketone (PEEK)) with two different cantilevers loading distances (10mm, 15mm). Material and methods: 20 frameworks were fabricated and divided into 4 groups (n=5): according to the material type, Peek, zirconia, and according to the cantilever loading distance (10), or (15) mm and a load-to-fracture test was used until complete fracture of specimens occurs. Results: The effect of material type and cantilever loading distance were statistically significant for the mean load-to-fracture values (P&lt; 0.05). The Zirconia group failed at higher fracture loads (817 N) than the Peek one (651 N). Frameworks with 10 mm cantilever loading distance failed at higher fracture loads than specimens with 15 mm. Conclusion: Peek is a suitable material for hybrid implant prosthesis (with distal cantilever in specific situations, and for zirconia the success chances are higher in these types of prosthesis when the distal cantilever length is kept at its minimal value (10 mm).

Evaluation of Tension and Deformation in a Mandibular Toronto Bridge Anchored on Three Fixtures Using Different Framework Materials, Abutment Systems, and Loading Conditions: A FEM Analysis.

The aim of this study was to investigate by finite element method analysis the behaviour of a three-implant mandible Toronto framework made by three different materials, with two abutment systems and two loading conditions. Three implants were virtually inserted in a mandible model in positions 3.6, 4.1, and 4.6. Three prosthetic framework bars with the same design and dimension (4.8 × 5.5 mm) were projected. The variables introduced in the computer model were the framework materials (glass fiber reinforced resin, Co-Cr, TiAl6V4), the abutment systems (Multi-Unit-Abutment [MUA]/OT-Bridge), and the loading conditions (500 N vertical load on all the framework area and 400 N on a 7-mm distal cantilever). The computer was programmed with physical properties of the materials as derived from the literature. Maximum tension and deformation values for each variable were registered at framework, screws, and abutment level and then compared. Metal frameworks Cr-Co and TiAl6V4 resulted in lower deformation than glass fiber-reinforced resin frameworks while presenting higher tension values. The OT-Bridge exhibited lower maximum tension and deformation values than the MUA system. The first loading condition reached higher tension and deformation values than the second and it resulted in more uniformly distributed load on all the framework area, especially with the OT-Bridge system. More rigid materials and OT-Bridge system decrease the deformation on the prosthetic components. Tension stresses are more uniformly distributed with glass fiber-reinforced resin, in the OT-Bridge system and avoiding cantilever loading.

Evaluation of Load Distribution in a Mandibular Model with Four Implants Depending on the Number of Prosthetic Screws Used for OT-Bridge System: A Finite Element Analysis (FEA).

In full-arch implant rehabilitations, when the anterior screw abutment channel compromises the aesthetic of the patient, the OT-Bridge system used with its Seeger rings may provide the necessary retention of the prosthesis. However, no studies have evaluated the forces generated at the Seeger level during loading. This Finite Element Analysis aims to investigate the mechanical behavior of Seeger rings in a mandibular model with four implants and an OT-Bridge system, used without one or two anterior prosthetic screws. A 400 N unilateral load was virtually applied on a 7 mm distal cantilever. Two different variables were considered: the constraint conditions using two or three screws instead of four and the three different framework materials (fiberglass reinforced resin, cobalt-chrome, TiAl6V4). The FEA analysis exhibited tensile and compressive forces on the Seeger closest to the loading point. With the resin framework, a tension force on abutment 3.3 generates a displacement from 5 to 10 times greater than that respectively expressed in metal framework materials. In a full-arch rehabilitation with four implants, the case with three prosthetic screws seems to be a safer and more predictable configuration instead of two. Considering the stress value exhibited and the mechanical properties of the Seeger, the presence of only two prosthetic screws could lead to permanent deformation of the Seeger in the screwless abutment closest to the loading point.

Distally Tilted Implants According to the All-on-Four® Treatment Concept for the Rehabilitation of Complete Edentulism: A 3.5-Year Retrospective Radiographic Study of Clinical Outcomes and Marginal Bone Level Changes.

Bone grafting procedures during the use of dental implants may be avoided by the use of tilted implants in the maxilla and the mandible; advantages of angled implants are associated with the extension of the distal cantilever, leading to better implant survival rates. However, the bending effect on the single tilting implants may increase the marginal bone stress. The purpose of the present study was to retrospectively assess the clinical success and proximal bone loss rate following the implantation of distally tilted implants according to the All-on-Four™ prosthetic concept—based on radiographic findings—in a single-center experience, in addition to the assessment of the outcomes in the context of various clinico-epidemiological correlates. During the study period, n = 36 patients (24 males and 12 females) with complete records of periapical radiographs, received a full-arch fixed bridge supported by two axial and two distal tilted implants; overall n = 144 and n = 144 implants (Nobel B) were place in the maxilla and mandibles of patients, respectively. Mean age of patients at the time of fixture installation was 58.75 ± 13.71 years; n =11 patients presented with relevant underlying conditions/habits. To assess peri-implant bone-level changes, matched and calibrated orthopantomogram (OPT) images were taken at follow-ups after 1.5 years, 2.5 years, and 3.5 years post-restoration, and marginal bone levels were assessed on the mesio- (MA) and disto-approximal (DA) aspects. All implants were successful, resulting in a 100% overall survival rate. The radiographic mean bone loss levels at baseline (mean ± SEM) were 0.181 ± 0.011 mm and 0.178 ± 0.017 mm in the maxilla and mandible, respectively, while by the 3.5-year mark, bone loss was 0.770 ± 0.029 mm and 0.713 ± 0.026 mm in the maxilla and mandible (p > 0.05), respectively; bone-level changes were significant over time (p = 0.035 and p = 0.033). Peri-implant bone loss was more aggressive around titled distal implants versus mesial actual position implants. The effect of smoking and other underlying conditions showed significantly higher (p < 0.05) bone resorption levels when assessed on an individual implant-level, while during patient-level analysis, only a tendency was shown for higher bone loss rates for both MA and DA implants (p > 0.05). Within its limitations, our study has concluded that the use of All-on-Four™ prosthetic concept for total arch rehabilitation yields higher bone loss in association with tilted implants and, in some cases, on the MA surfaces at vertically positioned implants after >40 months in function.

Analytical Modeling of the Interaction of a Four Implant-Supported Overdenture with Bone Tissue

Today, an interdisciplinary approach to solving the problems of implantology is key to the effective use of intraosseous dental implantations. The functional properties of restoration structures for the dentition depend significantly on the mechanical stresses that occur in the structural elements and bone tissues in response to mastication loads. An orthopedic design with a bar fixation system connected to implants may be considered to restore an edentulous mandible using an overdenture. In this study, the problem of the mechanics of a complete overdenture based on a bar and four implants was formulated. A mathematical model of the interaction between the orthopedic structure and jawbone was developed, and a methodology was established for the analytical study of the stress state of the implants and adjacent bone tissue under the action of a chewing load. The novelty of the proposed model is that it operates with the minimum possible set of input data and provides adequate estimates of the most significant output parameters that are necessary for practical application. The obtained analytical results are illustrated by two examples of calculating the equivalent stresses in implants and the peri-implant tissue for real overdenture designs. To carry out the final assessment of the strength of the implants and bone, the prosthesis was loaded with mastication loads of different localization. In particular, the possibilities of loading the prosthesis in the area of the sixth and seventh teeth were investigated. Recommendations on the configuration of the distal cantilever of the overdenture and the acceptable level and distribution of the mastication load are presented. It was determined that, from a mechanical point of view, the considered orthopedic systems are capable of providing long-term success if they are used in accordance with established restrictions and recommendations.

The effects of bar holder material, cantilever and vertical misfit on stresses in implant supported overdentures: Three dimensional finite element analysis

Background/Aim: The aim of this study is to examine with finite element analysis the distal bar extension, the bar substructure material type and the amount of bar substructure-abutment mismatch, and the stress caused by the implant at the surrounding bone tissue in bar-retained prostheses. Material and Methods: A bar-retained prosthesis model has been designed on three implants placed in the fully toothless lower jaw at the places of both canines and the midline. Bar holder according to distal cantilever lengths was modeled to be 0 mm, 8 mm and 14 mm. The vertical incompatibility of the bar holder substructure with the abutment was modeled to be 0 µm, 100 µm and 200 µm. A total of twenty-seven (3x3x3) different models were obtained with three different bar infrastructure materials (titanium, gold and chromium-cobalt). 150 N occlusal force was applied to the central fossa of the left 1st molar tooth with a rigid food stuff. Results: In the cortical bone, the highest maximum principle stress value (2.78 MPa) was analyzed around the anterior implant socket in the model 13 (gold, cantilever 0mm, misfit 100 µm). The highest von Mises stress value (343.43 MPa, which occurred at the selected joints in bar holders) was observed in model 27 (chrome-cobalt, cantilever 14mm, misfit 200 µm). Conclusions: When the length of the cantilever is 14 mm, it causes a significant increase in stress around the implant, especially near the cantilever. It has been observed that bar infrastructures with high elastic modulus create higher stress values.

Evaluation of misfit and stress distribution in implant-retained prosthesis obtained by different methods.

This study evaluated the vertical misfit, passivity, and stress distribution after tightening the screws of different prosthesis. Two implants were used to simulate the rehabilitation of partially edentulous mandible space from the second premolar to the second molar. 40 three-element screw-retained fixed dental prosthesis with distal cantilever were fabricated and divided into four groups according to the method of production of framework (n = 10): G1 = conventional casting one-piece framework, G2 = conventional casting sectioned and laser welding, G3 = conventional casting sectioned and tungsten inert gas (TIG) welding and G4 = framework obtained by CAD/CAM (computer-aided design/computer-aided manufacturing) system. The vertical misfits (both screws tightened) and the passive fit (one screw tightened) were measured under a comparator optical microscope. The data was submitted to Shapiro-Wilk test to enable comparison with ANOVA followed by Tukey with Bonferroni adjust (α = .05). The qualitative analysis of the stress distribution was performed by the photoelastic method. The vertical misfit (both screws tightened) of the G2 (24 μm) and G3 (27 μm) were significantly higher than G4 (10 μm) (p = 0,006). The passive fit (for the non-tightened) of the G1(64 μm) and G3 (61 μm) were significantly higher than the G4 (32 μm) (p=0,009). G1 showed high stress between the implants in the photoelastic analysis and G4 presented lower stress. In conclusion, CAD/CAM method results in less vertical misfit, more passivity, and consequently better stress distribution to the bone.

Single implant-supported two-unit cantilever fixed partial dentures in the posterior region: a retrospective case series with a mean follow-up of 6.5 years

BackgroundThe aim of this retrospective study was to evaluate the implant survival, clinical and radiographic outcomes, and patient satisfaction of single implant-supported two-unit cantilever fixed partial dentures in the posterior region.MethodsPatients who received a single implant-supported fixed partial denture with a cantilever in the posterior region between January 2004 and February 2018 were included. Survival rate of the implants and the fixed partial dentures and data regarding the marginal bone level, presence of plaque, calculus, bleeding on probing, mucosa health, pocket probing depth, and patient satisfaction were collected during an evaluation visit. Complications were recorded from the medical records.ResultsTwenty-three patients (mean age 64 ± 13 years) with 28 implants could be included in the study. The mean follow-up period was 6.5 ± 4.8 years at the time of data collection. The survival rate of the implants and fixed partial dentures was 100%. Mean marginal bone loss for the mesial and distal side of the implants was 0.41 mm (SD 1.18 mm) and 0.63 mm (SD 0.98 mm) respectively. A high prevalence of peri-implant-mucositis (89.3%) and peri-implantitis (17.9%) was observed as well as a limited number of technical complications. Patients were quite satisfied, as reflected by a mean VAS score of 94.0 ± 7.2 points (range 0–100) and a OHIP-NL49 score of 10.8 (range 0–196).ConclusionsSingle implant-supported fixed partial dentures with a mesial or distal cantilever can be a predictable treatment option in the posterior region, with stable peri-implant bone levels, minor technical complications, and very content patients. However, the prevalence of peri-implant mucositis and peri-implantitis was high.Trial registrationISRCTN, ISRCTN79055740, Registered on March 14, 2021 – —Retrospectively registered.

Cantilevered Versus non-cantilevered resilient bar attachment for 2-implant retained mandibular overdentures. A short term crossover study of chewing efficiency and bite force.

Aim of the study: This study compared chewing efficiency and maximum bite force between cantilevered and non-cantilevered resilient bar attachment used for 2-implant retained mandibular overdentures. Materials and methods: Eight completely edentulous participants (4 men, 4 women) with atrophied mandibular ridges receive 2 implants in the canine region. After 3 months, each patient received Hader bar with 7mm distal cantilevers and mandibular overdenture with 3 clips (CHB group). After another 3 months, distal cantilevers were sectioned and patients received Hader bar without cantilevers and mandibular overdentures with one clip (HB). Chewing efficiency (using unmixed fraction (UF) in a colored gum) and bite force were measured 3 months after using conventional dentures CD, CHB, and HB. Results: The highest unmixed fraction (UF) was noted with 5 cycles and the lowest number was noted with 50 cycles. UF decreased with the increase of number of chewing strokes. For all chewing strokes, the highest the UF was noted with CD, followed by HB, and the lowest UF was noted with CHB. At 30 and 50 strokes, there was a significant difference between each 2 groups, and HB showed significant higher UF than CHB. The highest maximum bite force was noted with CHB, followed by HB, and the lowest was noted with CD. Conclusion: it could be concluded that both cantilevered and non-cantilevered bar attachments for 2 implant overdentures achieved higher chewing efficiency and maximum bite force than conventional dentures in patients with atrophied mandibular ridges.

Framework Fracture of Zirconia Supported Full Arch Implant Rehabilitation: A Retrospective Evaluation of Cantilever Length and Distal Cross-Sectional Connection Area in 140 Patients Over an Up-To-7 Year Follow-Up Period.

To evaluate the relationship between different dimensional parameters in implant-supported monolithic zirconia fixed complete dental prostheses (IFCDPs) and the incidence of framework fracture in a large sample of cases in vivo. This retrospective observational study evaluated all patients rehabilitated with screw-retained zirconia IFCDPs between January 2013 and April 2019 at a private practice. The minimum follow-up period was 1 year after occlusal loading. Fractures were classified as: type I-fractures that happened between but not involving the two most posterior screw-access openings (SAOs) and type II-fractures of the distal cantilever. Cantilever length, distal connector cross-sectional area, and screw access opening length were measured using data obtained from digital scans. Logistic regression was performed to evaluate the relationship between types I and II fractures and the independent variables (dimensional parameters). Using the receiver operating characteristic curves, two parameters were identified to be useful for establishing a cut-off and predicting type II fractures. A total of 180 prostheses delivered to 140 patients were analyzed. Five implants failed in three patients: three before delivery of the definitive prostheses and two after. Ten prostheses failed (5.6% prosthetic failure rate): 2 because of implant failures, and 8 because of framework fractures. Five fractures were classified as type I and three as type II. Significant associations were found between cantilever length and type I fractures (Wald = 5.772, df = 1, p = 0.016), distal connector cross-sectional area and type II fractures (Wald = 3.806, df = 1, p = 0.051), and cantilever length and the total number of fractures (Wald = 6.117, df = 1, p = 0.013). Zirconia IFCDPs may be reliable medium-term solutions if some dimensional parameters are followed. The ratios between the cantilever length and cross-sectional connector area should be <0.51, while the ratio between the cantilever length and screw access opening length should be <1.48.

Fracture Load of CAD/CAM Fabricated Cantilever Implant-Supported Zirconia Framework: An In Vitro Study.

The fracture resistance of computer-aided designing and computer-aided manufacturing CAD/CAM fabricated implant-supported cantilever zirconia frameworks (ISCZFs) is affected by the size/dimension and the micro cracks produced from diamond burs during the milling process. The present in vitro study investigated the fracture load for different cross-sectional dimensions of connector sites of implant-supported cantilever zirconia frameworks (ISCZFs) with different cantilever lengths (load point). A total of 48 ISCZFs (Cercon, Degudent; Dentsply, Deutschland, Germany) were fabricated by CAD/CAM and divided into four groups based on cantilever length and reinforcement of distal-abutment: Group A: 9 mm cantilever; Group B: 9 mm cantilever with reinforced distal-abutment; Group C: 12 mm cantilever; Group D: 12 mm cantilever with reinforced distal-abutment (n = 12). The ISCZFs were loaded using a universal testing machine for recording the fracture load. Descriptive statistics, ANOVA, and Tukey’s test were used for the statistical analysis (p < 0.05). Significant variations were found between the fracture loads of the four ISCZFs (p = 0.000); Group-C and B were found with the weakest and the strongest distal cantilever frameworks with fracture load of 670.39 ± 130.96 N and 1137.86 ± 127.85 N, respectively. The mean difference of the fracture load between groups A (810.49 + 137.579 N) and B (1137.86 ± 127.85 N) and between C (670.39 ± 130.96 N) and D (914.58 + 149.635 N) was statistically significant (p = 0.000). Significant variations in the fracture load between the ISCZFs with different cantilever lengths and thicknesses of the distal abutments were found. Increasing the thickness of the distal abutment only by 0.5 mm reinforces the distal abutments by significantly increasing the fracture load of the ISCZFs. Therefore, an increase in the thickness of the distal abutments is recommended in patients seeking implant-supported distal cantilever fixed prostheses.

Comparative Analysis of the Stability of Prosthetic Screws under Cyclic Loading in Implant Prosthodontics: An In Vitro Study

Background: To compare the loss of preload in absence of loading and after a fixed number of cyclic loadings on 7-mm distal cantilever in two different connection systems using all-on-four prosthetic model. Methods: Two equal models of an edentulous mandible rehabilitated with all-on-four technique with two types of abutment system (MUA and OT-Bridge) supporting a hybrid prosthesis, were used. Initial torque values of the prosthetic fixing screw, after ten minutes from initial screw tightening and after 400,000 repeated loadings were registered using a mechanical torque gauge. Differences between initial and final torque values were reported for each anchoring system and the two systems were finally compared. Results: No statistically significant differences regarding the loss of preload between MUA and OT-Bridge system were found after 400,000 cyclic loadings; however, in MUA system it was found between anterior and posterior implant screws. A significant difference in preload loss was found only for MUA system comparing the initial screw torque to that measured after 10 min from the tightening in absence of cyclic loadings. Conclusions: Within the limits of the present study, MUA and OT-Bridge may be considered reliable prosthetic anchoring systems able to tolerate repeated cyclic occlusal loads on distal cantilever in all-on-four rehabilitation model without any significant loss of preload in screw tightening.